Commit 41edafdb authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by H. Peter Anvin
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x86/pvops: add a paravirt_ident functions to allow special patching 



Impact: Optimization

Several paravirt ops implementations simply return their arguments,
the most obvious being the make_pte/pte_val class of operations on
native.

On 32-bit, the identity function is literally a no-op, as the calling
convention uses the same registers for the first argument and return.
On 64-bit, it can be implemented with a single "mov".

This patch adds special identity functions for 32 and 64 bit argument,
and machinery to recognize them and replace them with either nops or a
mov as appropriate.

At the moment, the only users for the identity functions are the
pagetable entry conversion functions.

The result is a measureable improvement on pagetable-heavy benchmarks
(2-3%, reducing the pvops overhead from 5 to 2%).

Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 319f3ba5

arch/x86/include/asm/paravirt.h

+5 −0
Original line number Diff line number Diff line
@@ -388,6 +388,8 @@ extern struct pv_lock_ops pv_lock_ops; 
	asm("start_" #ops "_" #name ": " code "; end_" #ops "_" #name ":")



unsigned paravirt_patch_nop(void);

unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len);

unsigned paravirt_patch_ident_64(void *insnbuf, unsigned len);

unsigned paravirt_patch_ignore(unsigned len);

unsigned paravirt_patch_call(void *insnbuf,

			     const void *target, u16 tgt_clobbers,
@@ -1371,6 +1373,9 @@ static inline void __set_fixmap(unsigned /* enum fixed_addresses */ idx, 
}



void _paravirt_nop(void);

u32 _paravirt_ident_32(u32);

u64 _paravirt_ident_64(u64);



#define paravirt_nop	((void *)_paravirt_nop)



void paravirt_use_bytelocks(void);

arch/x86/kernel/paravirt.c

+66 −9
Original line number Diff line number Diff line
@@ -44,6 +44,17 @@ void _paravirt_nop(void) 
{

}



/* identity function, which can be inlined */

u32 _paravirt_ident_32(u32 x)

{

	return x;

}



u64 _paravirt_ident_64(u64 x)

{

	return x;

}



static void __init default_banner(void)

{

	printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
@@ -138,9 +149,16 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void *insnbuf, 
	if (opfunc == NULL)

		/* If there's no function, patch it with a ud2a (BUG) */

		ret = paravirt_patch_insns(insnbuf, len, ud2a, ud2a+sizeof(ud2a));

	else if (opfunc == paravirt_nop)

	else if (opfunc == _paravirt_nop)

		/* If the operation is a nop, then nop the callsite */

		ret = paravirt_patch_nop();



	/* identity functions just return their single argument */

	else if (opfunc == _paravirt_ident_32)

		ret = paravirt_patch_ident_32(insnbuf, len);

	else if (opfunc == _paravirt_ident_64)

		ret = paravirt_patch_ident_64(insnbuf, len);



	else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||

		 type == PARAVIRT_PATCH(pv_cpu_ops.irq_enable_sysexit) ||

		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
@@ -373,6 +391,45 @@ struct pv_apic_ops pv_apic_ops = { 
#endif

};



typedef pte_t make_pte_t(pteval_t);

typedef pmd_t make_pmd_t(pmdval_t);

typedef pud_t make_pud_t(pudval_t);

typedef pgd_t make_pgd_t(pgdval_t);



typedef pteval_t pte_val_t(pte_t);

typedef pmdval_t pmd_val_t(pmd_t);

typedef pudval_t pud_val_t(pud_t);

typedef pgdval_t pgd_val_t(pgd_t);





#if defined(CONFIG_X86_32) && !defined(CONFIG_X86_PAE)

/* 32-bit pagetable entries */

#define paravirt_native_make_pte	(make_pte_t *)_paravirt_ident_32

#define paravirt_native_pte_val		(pte_val_t *)_paravirt_ident_32



#define paravirt_native_make_pmd	(make_pmd_t *)_paravirt_ident_32

#define paravirt_native_pmd_val		(pmd_val_t *)_paravirt_ident_32



#define paravirt_native_make_pud	(make_pud_t *)_paravirt_ident_32

#define paravirt_native_pud_val		(pud_val_t *)_paravirt_ident_32



#define paravirt_native_make_pgd	(make_pgd_t *)_paravirt_ident_32

#define paravirt_native_pgd_val		(pgd_val_t *)_paravirt_ident_32

#else

/* 64-bit pagetable entries */

#define paravirt_native_make_pte	(make_pte_t *)_paravirt_ident_64

#define paravirt_native_pte_val		(pte_val_t *)_paravirt_ident_64



#define paravirt_native_make_pmd	(make_pmd_t *)_paravirt_ident_64

#define paravirt_native_pmd_val		(pmd_val_t *)_paravirt_ident_64



#define paravirt_native_make_pud	(make_pud_t *)_paravirt_ident_64

#define paravirt_native_pud_val		(pud_val_t *)_paravirt_ident_64



#define paravirt_native_make_pgd	(make_pgd_t *)_paravirt_ident_64

#define paravirt_native_pgd_val		(pgd_val_t *)_paravirt_ident_64

#endif



struct pv_mmu_ops pv_mmu_ops = {

#ifndef CONFIG_X86_64

	.pagetable_setup_start = native_pagetable_setup_start,
@@ -424,21 +481,21 @@ struct pv_mmu_ops pv_mmu_ops = { 
	.pmd_clear = native_pmd_clear,

#endif

	.set_pud = native_set_pud,

	.pmd_val = native_pmd_val,

	.make_pmd = native_make_pmd,

	.pmd_val = paravirt_native_pmd_val,

	.make_pmd = paravirt_native_make_pmd,



#if PAGETABLE_LEVELS == 4

	.pud_val = native_pud_val,

	.make_pud = native_make_pud,

	.pud_val = paravirt_native_pud_val,

	.make_pud = paravirt_native_make_pud,

	.set_pgd = native_set_pgd,

#endif

#endif /* PAGETABLE_LEVELS >= 3 */



	.pte_val = native_pte_val,

	.pgd_val = native_pgd_val,

	.pte_val = paravirt_native_pte_val,

	.pgd_val = paravirt_native_pgd_val,



	.make_pte = native_make_pte,

	.make_pgd = native_make_pgd,

	.make_pte = paravirt_native_make_pte,

	.make_pgd = paravirt_native_make_pgd,



	.dup_mmap = paravirt_nop,

	.exit_mmap = paravirt_nop,

arch/x86/kernel/paravirt_patch_32.c

+12 −0
Original line number Diff line number Diff line
@@ -12,6 +12,18 @@ DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %cr3, %eax"); 
DEF_NATIVE(pv_cpu_ops, clts, "clts");

DEF_NATIVE(pv_cpu_ops, read_tsc, "rdtsc");



unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)

{

	/* arg in %eax, return in %eax */

	return 0;

}



unsigned paravirt_patch_ident_64(void *insnbuf, unsigned len)

{

	/* arg in %edx:%eax, return in %edx:%eax */

	return 0;

}



unsigned native_patch(u8 type, u16 clobbers, void *ibuf,

		      unsigned long addr, unsigned len)

{

arch/x86/kernel/paravirt_patch_64.c

+15 −0
Original line number Diff line number Diff line
@@ -19,6 +19,21 @@ DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq"); 
DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");

DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");



DEF_NATIVE(, mov32, "mov %edi, %eax");

DEF_NATIVE(, mov64, "mov %rdi, %rax");



unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len)

{

	return paravirt_patch_insns(insnbuf, len,

				    start__mov32, end__mov32);

}



unsigned paravirt_patch_ident_64(void *insnbuf, unsigned len)

{

	return paravirt_patch_insns(insnbuf, len,

				    start__mov64, end__mov64);

}



unsigned native_patch(u8 type, u16 clobbers, void *ibuf,

		      unsigned long addr, unsigned len)

{

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